Was Mu'awiyah's, may Allah be pleased with him, bequeathing of power to Yazid a violation of the Guided Sunnah? And did he err in that? What were the sayings of the Companions contemporary to this act?

Mu'awiyah ibn Abi Sufyan was one of the best Muslim rulers, but he erred by appointing his son Yazid as his successor to the caliphate. Nevertheless, his virtues are not to be dismissed. 'Umar ibn al-Khattab appointed him over al-Sham (Syria), and 'Uthman ibn 'Affan confirmed him, and the people of al-Sham affirmed him for his justice and forbearance. The difference between his caliphate and the Rightly Guided Caliphate is that the Rightly Guided Caliphate was based on selection and consensus, whereas Mu'awiyah's caliphate was hereditary. To verify the sayings of the Companions regarding this event, one can refer to the books of scholars, such as "Al-'Awasim min al-Qawasim" by Ibn al-'Arabi al-Maliki, and the books of Sheikh Ali al-Sallabi in his defense of Mu'awiyah.